Doweling construction for rotary engine housing

ABSTRACT

The improved doweling construction for maintaining the housing parts of a rotary engine in their desired shape and relationship to each other comprises at least two dowels located on either side of the lobe junctions of the housing adjacent the top dead center (TDC) position of the rotor. One of the dowels is disposed to project through elongated openings in the end housing walls. The longitudinal axes of the openings are located so as to eliminate the resultant stress loading on the housing arising out of the differential rates of expansion between the end housing walls and the peripheral housing wall.

United States Patent Jones DOWELING CONSTRUCTION FOR ROTARY ENGINE HOUSING Primary ExaminerC. J. Husar Assistant ExaminerMichael Koczo, Jr.

Attorney, Agent, or FirmArthur Frederick; Victor D. Behn [57] ABSTRACT The improved doweling construction for maintaining the housing parts of a rotary engine in their desired shape and relationship to each other comprises at least two dowels located on either side of the lobe junctions of the housing adjacent the top dead center (TDC) position of the rotor. One of the dowels is disposed to project through elongated openings in the end housing walls. The longitudinal axes of the openings are located so as to eliminate the resultant stress loading on the housing arising out of the differential rates of expansion between the end housing walls and the peripheral housing wall.

5 Claims, 3 Drawing Figures U.S. Patent Dec. 9, 1975 Sheet 1 of2 3,924,581

U.S. Patent Dec. 9, 1975 Sheet 2 of2 3,924,581

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DOWELING CONSTRUCTION FOR ROTARY ENGINE HOUSING This invention relates to rotary engines and, more particularly, to an improved doweling construction for maintaining the housing components of a rotary engine in their desired shape and relationship under normal operating conditions.

In rotary engines of the Wankel type, such as exemplified in the U.S. patent to Wankel et al, No. 2,988,065, the engine is provided with a housing or casing within which a rotor is supported for eccentric rotation relative to the housing. The housing comprises two end walls separated by a peripheral wall having an inner trochoidal shaped surface, the housing elements being secured together by through bolts. Since in Wankel type internal combustion rotary engines combustion takes place in one region or area and subjects the housing in this high heat flux and pressure region to substantial thermal and mechanical stresses which tend to distort the housing elements and force them out of alignment with each other, a dowel structure is provided in this high heat flux region to prevent the distortion and misalignment of the housing elements. Such dowel structures are exemplified in the U.S. Pat. Nos. to Bentele et al, 3,007,460, Bonner, 3,269,372 and to Jones, 3,715,178. In all of these dowel structures, each of the dowels engage at their shank portions both the peripheral housing wall and the end housing walls to resist the principal resultant thermal and gas pressure loads which are directed substantially radially relative to the axis of rotor rotation. However, these doweling constructions have not satisfactorily prevented misalignment and distortions caused by the secondary resultant loading directed somewhat parallel to a tangential plane to the trochoidal surface adjacent the dowels due to the different rates of expansion of the housing end walls and the peripheral wall. This secondary loading is particularly pronounced in engine housings having end walls and a peripheral wall of different coefficients of expansion, as for example, an engine housing having a peripheral wall of aluminum and at least one end wall of cast iron.

SUMMARY The present invention therefore has for its prime purpose to provide an improved dowel structure for a rotary engine wherein the housing components or elements expand differently due to different thermal gradients and/or because of different coefficients of expansion. The improved dowel structure comprises at least two dowels located in the area or region of high stress and on opposite sides of the lobe junction of the housing adjacent the top dead center (TDC) position of the rotor and with one of the dowels disposed so that its shank portion projects through an elongated opening in each of the end walls of the housing. The longitudinal axes of the openings are located so as to extend somewhat parallel to an imaginary, substantially tangential line to the adjacent trochoidal surface of the peripheral housing wall. This elongated opening prevents transmission between the end walls and trochoid wall, via the dowel, of the resultant loading caused by differences in the thermal and pressure deflections and/or the different rates of thermal expansion between the peripheral wall and end walls.

It is therefore an object of this invention to provide an improved dowel structure for the housing of a rotary internal combustion engine having housing components of different relative growths under operating conditions.

It is another object of the present invention to provide in a rotary internal combustion engine an improved dowel structure which minimizes stress on and distortion of the peripheral wall of the housing due to the loading resulting from the difference in thermal growth between the housing peripheral wall and the end walls of the housing.

It is a further object of this invention to provide an improved dowel structure which permits the component housing walls of rotary internal combustion engine to be constructed of material having different coefficients of expansion.

BRIEF DESCRIPTION OF THE DRAWINGS The above and other objectives and advantages of the present invention will appear more fully hereinafter from a consideration of the detailed description which follows when taken together with the accompanying drawings wherein one embodiment of the invention is illustrated and in which:

FIG. 1 is an axial view of a rotary engine having a dowel structure according to this invention and with part of one end wall broken away for illustration purposes;

FIG. 2 is a cross-sectional view taken along line 2-2 of FIG. land on a somewhat enlarged scale; and

FIG. 3 is a fragmentary view in elevation of the dowel as shown in FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT Now referring to the drawings and particularly to FIG. 1 thereof, the reference number 10 generally designates a rotary internal combustion engine of the Wankel type, such as shown in the U.S. Pat. to Wankel et al, No. 2,988,065. The engine comprises a multi-part or multi-component outer body or housing 12 having a cavity within which an inner body or rotor 14 is eccentrically supported on a shaft 16 for planetary rotation. The housing 12 comprises two end walls 18 and 20 axially spaced apart by a peripheral wall 22 having an inner peripheral trochoidal surface 24. The end walls 18 and 2.0 and peripheral wall 22 are held together by a plurality of the bolts 25.

As shown, the housing cavity is of the two lobe type with the lobes meeting at lobe junctions 26 and 28 and therefore rotor 14 is shown as being generally triangular in profile with arcuate shaped shank portions 30 converging at apex portions 32. The rotor 14 and housing 12 define therebetween three working or combustion chambers 34, each of which successively expand and contract in volumetric size as the rotor planetates relative to the housing.

Fuel for combustion in the chambers is provided for by an intake port 36 in end wall 20, through which intake port 36 passes a mixture of fuel and air from a suitable source such as a carburetor. To ignite the compressed fuel and air mixture a spark plug 38 is secured in peripheral wall 22. Discharge of the spent products of combustion from chambers 34 is achieved by an exhaust port 39 located in peripheral housing wall 22. Of course other suitable means may be provided to achieve combustion in chambers 34 without departure from the scope and spirit of this invention. For example, only air may be introduced through intake port 36 with fuel injected in the chambers via an injector nozzle (not shown). Also, without departure from the scope and spirit of this invention, the engine may function as a diesel instead of being a spark ignited, Otto cycle engine, as shown. In any case, whether the engine operates as a diesel or four-phase Otto cycle engine, the combustion in each chamber 34 always occurs in the same region adjacent lobe junction 26, thus subjecting one area or region of housing 12 to high heat flux and gaseous pressure and the resultant thermal and mechanical stresses which tend to distort the housing components or elements and force them out of alignment with each other. These gas pressure and thermal loads in the peripheral housing are compensated for by a doweling construction according to this invention.

The improved dowel structure of this invention comprises at-least two dowel assemblies 40 and 40A in the high stress area on opposite sides of lobe junction 26. One or more additional dowel assemblies 40 may be located elsewhere on the housing (only one additional dowel assembly being shown in FIG. 1). Each dowel assembly 40 comprises a tubular dowel 42 which extends through aligned or registered holes in ears 44 formed integrally with end walls 18 and and peripheral wall 22. The dowel 42 is pressfitted or otherwise suitably secured in the holes in the ears of peripheral wall 22.

As best shown in FIGS. 2 and 3, dowel assembly 40A comprises a tubular dowel 42A, similar to dowels 42 of dowel asemblies 40, which projects through and is pressfitted in aligned holes 46 in ears 48 formed integrally with peripheral wall 22. Also, dowel 42A passes through an elongated opening or slot 50 in ears 52, similar to ears 44, formed integrally with end walls 18 and 20. Alternatively to pressfitting dowel 42A in place, dowel 42A may be clamped in position by a tie bolt (not shown) which extends therethrough and washers (not shown) disposed to abut opposite ends of dowel 42A and the nut and head of such tie bolt. As shown in FIG. 3, each of the slots 50 is dimensioned so that its width is such as to snugly receive dowel 42A and thereby permits dowel 42A. to absorb, together with one or more dowels 40, the radially directed primary resultant thermal and pressure load. The length of each of the slots 50 is such as to permit relative movement of the dowel and the end walls associated with each of the slots. Each slot 50 is located so that its longitudinal axis AA extends in a plane somewhat parallel to an imaginary tangent line T-T to the trochoidal surface adjacent dowel assembly 40A. This relationship of the longitudinal axis AA of the slot to the trochoidal surface 24 is important to permit relative movement of dowel 42A and end walls 18 and 20 and thereby relieve the resultant stress loading due to the different thermal gradients in end walls 18 and 20 and peripheral wall 22, which resultant loading stress is directed somewhat parallel to the imaginary tangent line T-T. This resultant stress loading is secondary to the primary thermal and gas pressure loads directed substantially radially relative to the axis of shaft 16. It has been found that this secondary resultant stress loading, unless relieved, causes distortion and misalignment of the housing end walls 18 and 20 and peripheral wall 22. By allowing relative movement of dowel 42A and slots 50 and hence relative movement between end walls 18 and 20 and peripheral wall 22 in this area of high stress and, under this secondary stress loading, the integrity of housing 12 is better maintained than in heretofore known dowel structures, such as exemplified in the U.S. Pat. Nos. to

4 Bentele et al 3,007,460, Bonner 3,269,372 and to Jones 3,715,178.

It has been found that this secondary stress load is due to the difference in thermal gradients between end walls 18 and 20 and peripheral wall 22 because different thermal gradients in those housing components occurs despite efforts at control through regulating liquid cooling flow rates through such housing walls. This secondary stress load is particularly pronounced where housing 12 comprises end walls constructed of material having a different coefficient of expansion than the material of which peripheral wall 22 is made.

It is to be understood that while the invention is described as applicable to an engine having a single rotor, it is equally applicable to engines having multiple rotors where each of the rotor cavities is defined by at least one intermediate wall.

It is believed now readily apparent that the herein described invention provides in a rotary internal combustion engine of the Wankel type an improved dowel structure for the engine housing which obviates distortion and misalignment due to the different growth rates of the housing elements or by reason of housing elements made of material having different coefficients of expansion. It is a dowel structure which compensates for both primary and secondary stress loadings.

Although but one embodiment of the invention has been illustrated and described in detail, it is to be expressly understood that the invention is not limited thereto. Various changes can be made in the arrangement of parts without departing from the spirit and scope of the invention as the same will now be understood by those skilled in the art.

What is claimed is:

1. In a rotary internal combustion engine having a housing consisting of a pair of spaced, substantially parallel end walls and a peripheral wall having a trochoidal shaped inner surface, the end and peripheral walls defining therebetween a cavity in which a rotor is mounted for planetary rotation and which defines with said walls working chambers which successively expand and contract in volumetric size as the rotor rotates relative to the housing, wherein combustion occurs in the working chambers adjacent one area of the housing exposing that area to relatively higher temperatures and pressures than in the remainder of the housing whereby said area is subjected to high stresses, and wherein at least one end wall and the peripheral wall have different rates of expansion than the other housing walls which differential expansion would tend to subject the housing to additional stress, an improved dowel structure for maintaining alignment of said end walls and peripheral wall, comprising:

a. at least two dowels disposed in the high stress area on opposite sides of the lobe junction in this area of high stress and extending through said end walls and peripheral wall;

b. one of the dowels being disposed to project through an elongated opening in the end wall having a different rate of expansion; and

c. said elongated opening having a longitudinal axis extending in a direction to obviate the additional resultant stress loading on the housing arising out of the differential rate of expansion between the end wall and said peripheral wall.

2. The apparatus of claim 1 wherein said peripheral wall and said end wall is made of material having different coefficients of expansion.

ceives the resultant stress loads extending in a radial direction relative to the axis of rotation of said rotor.

5. The apparatus of claim 1 wherein said dowel is hollow and wherein a tie bolt extends therethrough. 

1. In a rotary internal combustion engine having a housing consisting of a pair of spaced, substantially parallel end walls and a peripheral wall having a trochoidal shaped inner surface, the end and peripheral walls defining therebetween a cavity in which a rotor is mounted for planetary rotation and which defines with said walls working chambers which successively expand and contract in volumetric size as the rotor rotates relative to the housing, wherein combustion occurs in the working chambers adjacent one area of the housing exposing that area to relatively higher temperatures and pressures than in the remainder of the housing whereby said area is subjected to high stresses, and wherein at least one end wall and the peripheral wall have different rates of expansion than the other housing walls which differential expansion would tend to subject the housing to additional stress, an improved dowel structure for maintaining alignment of said end walls and peripheral wall, comprising: a. at least two dowels disposed in the high stress area on opposite sides of the lobe junction in this area of high stress and extending through said end walls and peripheral wall; b. one of the dowels being disposed to project through an elongated opening in the end wall having a different rate of expansion; and c. said elongated opening having a longitudinal axis extending in a direction to obviate the additional resultant stress loading on the housing arising out of the differential rate of expansion between the end wall and said peripheral wall.
 2. The apparatus of claim 1 wherein said peripheral wall and said end wall is made of material having different coefficients of expansion.
 3. The apparatus of claim 1 wherein the longitudinal axis of the elongated opening extends somewhat parallel to an imaginary tangential line to the trochoidal surface adjacent the elongated opening.
 4. The apparatus of claim 1 wherein said elongated opening is so dimensioned that an associated dowel receives the resultant stress loads extending in a radial direction relative to the axis of rotation of said rotor.
 5. The apparatus of claim 1 wherein said dowel is hollow and wherein a tie bolt extends therethrough. 